Abstract
We have discovered a new gravitational lens in the Cosmic Lens All-Sky Survey. The lens B1555+375 is a four-image system with a maximum separation of 0
42. VLA and MERLIN radio observations show these images in a characteristic quadruple-lens configuration. Optical imaging with the Keck II Telescope at R band shows a faint extended object. We estimate the combined emission from the lens and background source to be R = 25 mag. Observations at H band with the William Herschel Telescope also detected this extended object. The combined lens and background source magnitude was measured to be H = 19 mag. Presently, redshifts for both the lensing galaxy and background source are undetermined. We conclude that one or more of the following are true: the lens galaxy is sub-L*, it has z > 0.5, or it is highly reddened. The observed MERLIN component positions and flux densities can be well described by a lens model based on a singular isothermal ellipsoid mass distribution. Our best-fit lens model has a reduced χ2 of 2.6. High-resolution VLA radio observations should help to constrain the lens model further.
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Footnotes
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Based on observations made with the National Radio Astronomy Observatory (NRAO), which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.; with the Multi-Element Radio-linked Interferometer Network (MERLIN), which is a national facility operated by the Nuffield Radio Astronomy Laboratories, Jodrell Bank, University of Manchester, on behalf of the UK Particle Physics and Astronomy Research Council; with the William Herschel Telescope (WHT), which is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias; and with the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation.